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Substrate specificity and contribution of the glycosyltransferase UGT71A15 to phloridzin biosynthesis

Affiliation
Institute of Chemical Engineering, Vienna University of Technology, Getreidemarkt 9, 1060 Vienna, Austria
Gosch, C.;
GND
128593652
Affiliation
Julius Kühn-Institute (JKI), Federal Research Centre for Cultivated Plants, Institute for Fruit Breeding, Dresden, Germany
Flachowsky, Henryk;
Affiliation
Institute of Chemical Engineering, Vienna University of Technology, Getreidemarkt 9, 1060 Vienna, Austria
Halbwirth, H.;
Affiliation
Institute of Chemical Engineering, Vienna University of Technology, Getreidemarkt 9, 1060 Vienna, Austria
Thill, J.;
Affiliation
Institute of Chemical Engineering, Vienna University of Technology, Getreidemarkt 9, 1060 Vienna, Austria
Mjka-Wittmann, R.;
Affiliation
Unit Fruit Science, Technische Universita¨t Mu¨nchen, Freising, Germany
Treutter, D.;
GND
1059141744
Affiliation
Julius Kühn-Institute (JKI), Federal Research Centre for Cultivated Plants, Institute for Resistance Research and Stress Tolerance, Quedlinburg, Germany
Richter, Klaus;
GND
1059103400
Affiliation
Julius Kühn-Institute (JKI), Federal Research Centre for Cultivated Plants, Institute for Fruit Breeding, Dresden, Germany
Hanke, Magda-Viola;
Affiliation
Institute of Chemical Engineering, Vienna University of Technology, Getreidemarkt 9, 1060 Vienna, Austria
Stich, K.

The dihydrochalcone phloridzin (phloretin 2′-O-glucoside) is the most abundant phenolic compound in apple trees (Malus × domestica) and was also discussed to have an influence on the pathogen defence by shifting the dihydrochalcone profile from the glucosides to the more active aglycones. The final step in the biosynthesis of phloridzin is the glycosylation of phloretin at position 2′. Three cDNA clones from apple encoding glycosyltransferases are available which are able to catalyze the reaction in vitro. We investigated the possible role of glycosyltransferase UGT71A15 in phloridzin biosynthesis. The recombinant enzyme showed broad substrate acceptance but highest activities were observed with flavonols. Specific activities and the kinetic data indicated that phloretin is not the preferred native substrate of the UGT71A15. However, an increase of the molar ratio phloridzin:phloretin was found in transgenic lines, indicating a physiological relevance of UGT71A15 in planta, although a decrease of the total amount of dihydrochalcones in the majority of the samples was found. Unexpectedly, the increase of the phloridzin:phloretin ratio was not reflected by an increase of the total glucosyltransferase activities. In contrast, the majority of transgenic plants showed a reduced glucosylating activity with both phloretin and quercetin as a substrate, but the observed activity changes in a given sample were not similar for the two substrates. An increased susceptibility of M. robusta against the fire blight causing bacterium E. amylovora as a result of UGT71A15 overexpression could not be observed. Overexpression of UGT71A15 in transgenic apple trees also did not lead to morphological changes.

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